Although much knowledge exists concerning human perceptual abilities and disabilities, there is little direct information about the underlying brain mechanisms, principally because many of the most powerful neurophysiological methods cannot be used on humans. Recently, a way to improve this situation has arisen with the development of functional magnetic resonance imaging (fMRI), a technique that permits sites of brain activation to be localized in normal human subjects. The proposed study will explore a specific aspect of human auditory perception as an entree into using fMRI to investigate sound localization processing. This perception is lateralization, a particular binaural phenomenon that has clear electrophysiological correlates in humans. The goal of this study is to elucidate the role of the cortex in human lateralization using fMRI. Two sets of experiments are proposed. The first will provide measurements of human cortical activity in response to stimuli used routinely in psychophysical investigations of lateralization. These experiments should help bridge the gap between animal and human work on sound lateralization and should also help elucidate the relationship between fMRI and electrophysiological measures. The second set of experiments will provide measurements of human cortical activity for stimuli that evoke a shift in perceived sound location, or "lateralization shift's. From these is should be possible to identify cortical areas involved in lateralization. The proposed work will lay a general groundwork for any future fMRI investigations of auditory processing in both normal humans and patients with hearing or neurological disorders.